Updated Aug 2026
Ohio Lake Water Quality
Water quality grades for 52 monitored lakes across 28 counties.
Ohio has 52 graded lakes in our dataset, sampled across 28 counties, drawing on monitoring by the Ohio Environmental Protection Agency plus federal and volunteer measurements. A-grade lakes are scarce in Ohio: about 4% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
A meaningful share of the state's monitored lakes register as hypereutrophic — heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. Union ranks highest on average county grade (A). Clark sits lowest. With only 28 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
All 52 Ohio lakes in the index: 38 (73.1%) carry an A–F grade and 14 (26.9%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
Where to stay near Ohio
Top-rated places to stay near Ohio
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Top-Graded Ohio Lakes
The highest water-quality grades in Ohio — clarity, depth, and A-F grade at a glance.
Lake Map
Explore Ohio Lakes
Ohio reports, fishing & travel
Ohio's cleanest and most-polluted lakes, ranked A–F
Species activity outlook by water temperature and season
Where to stay at Ohio's top lakes, each with its grade
Best-graded lakes within 50 miles of Columbus
Best-graded lakes within 50 miles of Cleveland
Reservoirs in Ohio
View all 7 reservoirs →7 of 52 Ohio lakes (13%) are man-made reservoirs in the USACE National Inventory of Dams. 7 carry a High or Significant hazard rating. The oldest matched dam dates to 1936.
EPA-Impaired Lakes in Ohio
View all 17 impaired lakes →17 of 52 Ohio lakes (33%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 14 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Ohio Fishing & Recreation
Licenses, regulations, records, and where to fish across Ohio.
Counties
All 28 Ohio counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Ohio Lake Water Quality Dataset (2026)
Every graded Ohio lake in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
Top 25 Cleanest Lakes
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | AAlum Creek Lake | Delaware | A | No recent samples | Mesotrophic | Not recorded |
| 2 | AMarysville Upground Reservoir | Union | A | No recent samples | Mesotrophic | Not recorded |
| 3 | BPowers Reservoir | Crawford | B | No recent samples | Eutrophic | Not recorded |
| 4 | BLost Creek Reservoir | Allen | B | No recent samples | Eutrophic | Not recorded |
| 5 | CTiffin R Lake | Defiance | C | No recent samples | Mesotrophic | Not recorded |
| 6 | CFremont Reservoir | Sandusky | C | No recent samples | Eutrophic | Not recorded |
| 7 | CNew Lexington Reservoir | Perry | C | No recent samples | Mesotrophic | Not recorded |
| 8 | CFindlay Reservoir | Hancock | C | No recent samples | Mesotrophic | Not recorded |
| 9 | COttawa R Lake | Allen | C | No recent samples | Mesotrophic | Not recorded |
| 10 | CFerguson Reservoir | Allen | C | No recent samples | Eutrophic | Not recorded |
| 11 | CWilliams Reservoir | Allen | C | No recent samples | Eutrophic | Not recorded |
| 12 | DCaesar Creek Lake | Warren | D | 3.2 ft | Eutrophic | Not recorded |
| 13 | DMaumee R Upst Independence Dam Lake | Defiance | D | No recent samples | Hypereutrophic | Not recorded |
| 14 | DUpper Sandusky Reservoir | Wyandot | D | No recent samples | Eutrophic | Not recorded |
| 15 | DBurr Oak Reservoir | Morgan | D | No recent samples | Eutrophic | Not recorded |
| 16 | DLake Logan | Hocking | D | No recent samples | Eutrophic | Not recorded |
| 17 | DSalem Reservoir | Columbiana | D | No recent samples | Mesotrophic | Not recorded |
| 18 | DMetzger Reservoir | Allen | D | No recent samples | Eutrophic | Not recorded |
| 19 | DTwin Lakes Reservoir | Allen | D | No recent samples | Eutrophic | Not recorded |
| 20 | DOttawa Reservoir | Putnam | D | No recent samples | Eutrophic | Not recorded |
| 21 | DAmann Reservoir | Morrow | D | No recent samples | Hypereutrophic | Not recorded |
| 22 | FBuck Creek Lake | Clark | F | 2.5 ft | Hypereutrophic | Not recorded |
| 23 | FBuck Creek Lake | Clark | F | 2.3 ft | Hypereutrophic | Not recorded |
| 24 | FBuck Creek Lake | Clark | F | 2.5 ft | Hypereutrophic | ✓ Public |
| 25 | FBuck Creek Lake | Clark | F | 2 ft | Hypereutrophic | ✓ Public |
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FHoover Reservoir | Delaware | F | No recent samples |
| 2 | FHoover Reservoir | Franklin | F | No recent samples |
| 3 | FBresler Reservoir | Allen | F | No recent samples |
| 4 | FO'Shaughnessy Reservoir Lake | Delaware | F | No recent samples |
| 5 | FAmicks Reservoir | Morrow | F | No recent samples |
| 6 | FAlum Creek Lake | Delaware | F | No recent samples |
| 7 | FSt Joseph Lake | Perry | F | No recent samples |
| 8 | FGrand Lake St Marys @ Intake | Mercer | F | No recent samples |
| 9 | FSomerset Reservoir | Perry | F | No recent samples |
| 10 | FSpring Valley Lake Lake | Columbiana | F | No recent samples |
| 11 | FGrand Lake St Marys | Mercer | F | No recent samples |
| 12 | FAuglaize R Lake | Paulding | F | No recent samples |
| 13 | FTappan Lake | Harrison | F | 1.8 ft |
| 14 | FBuck Creek Lake | Clark | F | 2 ft |
| 15 | FBuck Creek Lake | Clark | F | 2.5 ft |
| 16 | FBuck Creek Lake | Clark | F | 2.3 ft |
| 17 | FBuck Creek Lake | Clark | F | 2.5 ft |
| 18 | DAmann Reservoir | Morrow | D | No recent samples |
| 19 | DOttawa Reservoir | Putnam | D | No recent samples |
| 20 | DTwin Lakes Reservoir | Allen | D | No recent samples |
| 21 | DMetzger Reservoir | Allen | D | No recent samples |
| 22 | DSalem Reservoir | Columbiana | D | No recent samples |
| 23 | DLake Logan | Hocking | D | No recent samples |
| 24 | DBurr Oak Reservoir | Morgan | D | No recent samples |
| 25 | DUpper Sandusky Reservoir | Wyandot | D | No recent samples |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
The top-graded lake in every state we cover, picked grade-first with water clarity as the tie-breaker — plus the states whose winner is still not clean.
State-by-state Secchi champions: the clearest measured lake in each U.S. state we grade, which is not the same as the cleanest nutrient grade.
A data snapshot of the lakes we grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.